The present invention relates to an anode element for use in a cathodic protection system and provided with a metal tube, the one extremity of which is pointed and the other extremity of which is adapted to be acted upon by an impactor, an electrically conductive rod disposed within the tube aligned with the center line of the tube and spaced from the tube wall and having a length smaller than the tube, a connecting cable connected to the rod and extending to the outside of the tube via a passage provided in the tube wall, and a quantity of granular carbon-containing filling material within the tube, the filling material being in contact with the rod and with the tube wall, which filling material can be kept within the tube by means of a disk-shaped sealing provided at the other extremity of the tube.
An anode element of this type is known from U.S. Pat. No. 2,053,214 issued to R. C. BROWN, on Sept. 1, 1936. In said known anode element, the rod preferably consists of pressed graphite, and in the vicinity of the other, dull extremity of the tube the end of the rod and an end of the connecting cable are enclosed in the disk-shaped sealing which is supported all around against the inner wall of the tube, the sealing being gas-impermeable and consisting of carbon and asphalt or any other suitable mastic material. The rod may also consist of copper or steel with a covering of granular silicon carbide or zirconium. Such a form of construction of the known anode element using a porous filling and a porous surface of the rod is aimed to extend the disintegration time of, in particular, the rod.
A heavy metal drive cap, for example of wrought iron, is placed over the dull extremity of the tube. The connecting cable is routed to the outside of the tube via aligned passages which are formed in the tube wall of the dull extremity of the tube and in the cap flange extending over this extremity.
This known anode element has the drawback that it is not sufficiently adapted to be driven into the ground completely. During the driving operation, the cap provided on the dull extremity of the tube would cause an undesirable, great resistance with the surrounding earth, while the connecting cable may be damaged by the surrounding earth during said driving operation, particularly so if the ground would contain hard objects with sharp edges, such as pieces of rock. For similar reasons, the known anode element is not suitable as a succeeding element to be driven into a shaft already present, as a result of an anode element previously driven into the ground. The connecting cable of each anode element previously driven in, will then almost certainly be damaged by each anode element subsequently driven into the same shaft.
In order to obtain a greater current density of the core or rod provided within the tube and to extend the useful life of the anode element during its use within the ground, nowadays a rod is preferred consisting of another material, for instance silicon iron, which in addition can be easily cast into a desired form and subsequently machined. However, a rod formed from such a material having initial dimensions corresponding to a desired current density and lifetime thereof is relatively heavy with respect to the rod used in the known anode element. The disk-shaped sealing member used in the dull extremity ensuring a mechanical and electrical connection between the connecting cable, the rod and the inner wall of the tube is, therefor, not sufficiently suited to accommodate therein an end of a relatively heavy rod. If driving the anode element would take place by means of an impactor, which would be desirable for deep penetration, there would be the danger of breaking the mechanical and/or electrical connection.
Although a rod of silicon iron is less brittle than a rod of graphite, there would, when using a rod of silicon iron in the known anode element, still be the danger of the rod breaking during impacting, thus resulting in a smaller efficiency and shorter useful lifetime. This is due to the fact that in the case of the known anode element the rod is connected relatively rigidly to the tube by means of the disk-shaped sealing member. The danger of cracking or breaking is then greater to the extent that a greater force of impact is to be exerted upon the dull tube extremity, for example, when driving the element into the ground over a relatively large distance and/or when the earth is rocky and/or the anode element would be adapted to be driven in conjunction with several others in a line.
German Pat. No. 2,207,061 issued to DALE, OLAV TUMBA, on Aug. 31, 1972, discloses an anode element consisting of a tube having a pointed extremity in which there is centrally disposed a rod, for example of copper, extending from the one extremity to the other extremity. In the tube point area, the rod is centered in a plastic centering piece, and at the dull extremity of the tube the rod is contained in a disk-shaped sealing of insulating, hardened material. The filling material provided within the tube consists of a hardened mixture of for instance 50% epoxy resin and 50% graphite powder. The connecting cable connected to the rod in the disk-shaped sealing member is routed aligned with the rod out of the dull extremity of the tube. To afford driving this known anode element into the ground by means of an impactor, an adaptor is placed over the dull extremity of the tube, the adaptor being provided in longitudinal direction with a slot for cable passage. In order to protect the cable over the entire shaft length above the anode element, while the latter is being driven, the adaptor length should be at least equal to the length of the portion of the shaft which is attained when the anode element reaches its final position. Consequently, driving the anode element into the ground over a large distance requires an adaptor having an impractical length. Said known anode element is not suitable either to be placed, possibly using the adaptor, after an anode element previously placed into the same shaft, because in such event the connecting cable of each previously placed anode element is almost certain to be damaged while a subsequent anode element is being driven in. Since the entire anode element mainly consists of undeformable, mutually immovable material, the known anode element is not suitable either for a rod to be used which consists of relatively brittle material, such as silicon iron. For, during the driving of the anode element, the rod could crack, as a result of which the efficiency and useful lifetime of the element would be reduced.
In addition, each of the known anode elements described hereinbefore has the drawback that the disk-shaped sealing member consists of a material that is gas-impermeable, which impedes proper functioning of the anode element.